According to IPCC's Third Assessment Report:
• 'There is new and stronger evidence that most of the warming observed over the past 50 years is attributable to human activities.
• Human influences are expected to continue to change atmospheric composition throughout the 21st century.'
The greenhouse gas making the largest contribution from human activities is carbon dioxide (CO2). It is released by burning fossil fuels and biomass as a fuel; from the burning, for example, of forests during land clearance; and by certain industrial and resource extraction processes.
• 'Emissions of CO2 due to fossil fuel burning are virtually certain to be the dominant influence on the trends in atmospheric CO2 concentration during the 21st century.
• Global average temperatures and sea level are projected to rise under all (...) scenarios.'
The ultimate objective of the UN Framework Convention on Climate Change, which has been accepted by 189 nations, is to achieve '(...) stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system', although a specific level has yet to be agreed.
Technological options for reducing net CO2 emissions to the atmosphere include:
• reducing energy consumption, for example by increasing the efficiency of energy conversion and/or utilization (including enhancing less energy-intensive economic activities);
• switching to less carbon intensive fuels, for example natural gas instead of coal;
• increasing the use of renewable energy sources or nuclear energy, each of which emits little or no net CO2;
• sequestering CO2 by enhancing biological absorption capacity in forests and soils;
• capturing and storing CO2 chemically or physically.
The first four technological options were covered in earlier IPCC reports; the fifth option, the subject of this report, is Carbon dioxide Capture and Storage (CCS). In this approach, CO2 arising from the combustion of fossil and/or renewable fuels and from processing industries would be captured and stored away from the atmosphere for a very long period of time. This report analyzes the current state of knowledge about the scientific and technical, economic and policy dimensions of this option, in order to allow it to be considered in relation to other options for mitigating climate change.
At present, the global concentration of CO2 in the atmosphere is increasing. If recent trends in global CO2 emissions continue, the world will not be on a path towards stabilization of greenhouse gas concentrations. Between 1995 and 2001, average global CO2 emissions grew at a rate of 1.4% per year, which is slower than the growth in use of primary energy but higher than the growth in CO2 emissions in the previous 5 years. Electric-power generation remains the single largest source of CO2 emissions, emitting as much CO2 as the rest of the industrial sector combined, while the transport sector is the fastest-growing source of CO2 emissions. So meeting the ultimate goal of the UNFCCC will require measures to reduce emissions, including the further deployment of existing and new technologies.
The extent of emissions reduction required will depend on the rate of emissions and the atmospheric concentration target. The lower the chosen stabilization concentration and the higher the rate of emissions expected in the absence of mitigation measures, the larger must be the reduction in emissions and the earlier that it must occur. In many of the models that IPCC has considered, stabilization at a level of 550 ppmv of CO2 in the atmosphere would require a reduction in global emissions by 2100 of 7-70% compared with current rates. Lower concentrations would require even greater reductions. Achieving this cost-effectively will be easier if we can choose flexibly from a broad portfolio of technology options of the kind described above.
The purpose of this report is to assess the characteristics of CO2 capture and storage as part of a portfolio of this kind. There are three main components of the process: capturing CO2, for example by separating it from the flue gas stream of a fuel combustion system and compressing it to a high pressure; transporting it to the storage site; and storing it. CO2 storage will need to be done in quantities of gigatonnes of CO2 per year to make a significant contribution to the mitigation of climate change, although the capture and storage of smaller amounts, at costs similar to or lower than alternatives, would make a useful contribution to lowering emissions. Several types of storage reservoir may provide storage capacities of this magnitude. In some cases, the injection of CO2 into oil and gas fields could lead to the enhanced production of hydrocarbons, which would help to offset the cost. CO2 capture technology could be applied to electric-power generation facilities and other large industrial sources of emissions; it could also be applied in the manufacture of hydrogen as an energy carrier. Most stages of the process build on known technology developed for other purposes.
There are many factors that must be considered when deciding what role CO2 capture and storage could play in mitigating climate change. These include the cost and capacity of emission reduction relative to, or in combination with, other options, the resulting increase in demand for primary energy sources, the range of applicability, and the technical risk. Other important factors are the social and environmental consequences, the safety of the technology, the security of storage and ease of monitoring and verification, and the extent of opportunities to transfer the technology to developing countries. Many of these features are interlinked. Some aspects are more amenable to rigorous evaluation than others. For example, the literature about the societal aspects of this new mitigation option is limited. Public attitudes, which are influenced by many factors, including how judgements are made about the technology, will also exert an important influence on its application. All of these aspects are discussed in this report.
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